This invention relates in general to apparatus for pelletizing solid waste and more specifically to control systems which aid in the production of compacted shredded refuse to form a coherent pellet which remains intact as it is pyrolyzed in a vertical shaft furnace.
During the past several years considerable effort has gone into developing new technology for disposing of solid refuse in an environmentally acceptable manner and at the same time recovering, insofar as possible, the useful resources contained therein. One such process is described in U.S. Pat. No. 3,729,298 wherein solid refuse is fed directly into a vertical shaft furnace in which the combustible portion of the refuse is pyrolyzed -- principally to a fuel gas consisting of carbon monoxide and hydrogen -- and in which the uncombustible portion of the refuse is fluidized to molten metal and slag.
An improvement on the process described in the above-mentioned U.S. patent is described and claimed by J. E. Anderson in U.S. patent application Ser. No. 675,935, filed Apr. 12, 1976, now U.S. Pat. No. 4,042,345, incorporated herein by reference. This process requires that the refuse be compacted into pellets that are sufficiently strong to remain intact as they move down through the drying and pyrolysis zones of the furnace. Anderson has found that in order to have a refuse pellet which is sufficiently strong to remain coherent, i.e. intact, his process requires that it have a specified minimum density.
Anderson has also discovered that if the refuse pellets are sufficiently dense to have the necessary structural strength, then the drying and pyrolysis reactions become limited by the rate of heat transfer and diffusion within the pellets, and that in order to obtain a satisfactory process, the ratio of the surface area to the volume of the pellets should be greater than a specified minimum.
A system capable of producing pellets of these required characteristics is described in copending application Ser. No. 675,934, filed Apr. 12, 1976, now abandoned. Briefly and generally, this system illustratively employs a pair of parallel alternately actuated compactor tubes, each tube including: (1) a hydraulic ram housed at one end of the tube for compacting the refuse; (2) an inlet port at an intermediate section of the tube; and (3) a compacting section and outlet at the other end of the tube, from which the compacted pellets issue.
The inlet ports of the compacting tubes are supplied from a common chute fed from a refuse conveyor system, and of particular relevance to the invention herein, is the incorporation in such chute of a reciprocating member, e.g. a vane which cyclically sweeps the refuse in the chute alternatively to one compactor inlet port and then the other. Besides directing the refuse to each compactor, the cyclical feed member also performs a pre-packing function and serves to inhibit back flow from the compactor inlet port.
In addition, the reciprocating action of the cyclical feed member is a reflection of system flow and changes in such action signal an incipient jam, i.e., the occurrence or onset of a disruption in the flow of material through the multiple channel compactor. The present invention provides control means for exploiting the phenomenon to inhibit such jams.
Thus, the occurrence of a transient excess in the amount of refuse fed to the chute will, if of sufficient magnitude, alter the cyclical action of the vane. Although the vane will continue to oscillate, its period and/or displacement will be altered by the transient excess and these departures from the norm are detected by the control circuit, causing an interruption in the feed of refuse. This interruption in effect gives the vane an opportunity over succeeding cycles to dispose of the excess load by feeding it to the two compactors. As this is accomplished, the vane's periodicity and/or displacement return to normal. This is detected by the control circuit which thereupon restarts the refuse feed operation.
A similar sequence of events will be precipitated by a material increase of density in the refuse fed to the chute.